The invention relates to a high strength, precipitation hardening, non-magnetic austenitic stainless steel alloy in which the austenite phase is sufficiently stable so that it does not transform to the ferromagnetic martensite phase even under substantial reduction, for instance by cold rolling of sheet or drawing of wire made from the alloy.
The rapid development within the computer and electronics industry has created an increased demand for materials with combinations of properties not previously considered or easily achievable such as, for example, the combination of high mechanical strength and a non-magnetic structure for materials to be used in spring applications where the material is required to be magnetically inert. For many of these products, the manufacture involves various forming (reducing) steps. Since it is common knowledge that increased strength also leads to impaired ductility, it is an essential advantage if the forming steps can be carried out in as soft condition as possible and the required strength ultimately needed can be achieved by a simple heat treatment.
Among these high strength stainless steels, the so-called non-stable austenitic spring steels, SS 2331 with a typical nominal analysis of 17 Cr, 7 Ni, 0.8 Si, 1.2 Mn, 0.1 C and 0.03 N are in a special position because of their combination of high strength and good corrosion properties.
The very high strength achievable with this type of steel depends from the fact that the (non-magnetic) austenitic structure is transformed during deformation to (ferromagnetic) martensite, a phase that has exceptional hardness. When the amount of alloying elements (primarily Ni and Mo) is increased as in such types SS 2343/2353, the tendency for the formation of deformation martensite is reduced but the possibility of achieving high strength is thereby also reduced. Furthermore, the use of this type of steel leads to high alloying costs because the high amounts of nickel and molybdenum.